The nature of onboard equipment varies greatly and its energy consumption varies greatly over time. By way of example, the internal air-conditioning and lighting systems are in almost continuous operation whereas redundant safety systems such as controls of airfoils, are used only exceptionally.
Generally, the craft employs three-phase electrical generators allowing power to be supplied to all the items of onboard electrical equipment, called loads subsequently. These generators deliver for example a voltage of 115 V at a frequency of 400 Hz to an AC bus of the craft. Aboard a craft there are for example one or more main generators. These are rotating electric machines driven by the engine or engines of the craft. There is also an auxiliary generator well known in the literature by the name “auxiliary power unit” driven by a turbine dedicated to this generator and supplying power to the craft when it is on the ground or in flight. Numerous airports employ ground power generators or ground-based electrical units making it possible to power the AC bus of the craft directly, so as to avoid calling upon the auxiliary generator. This ground power unit is for example installed in proximity to the craft on the ground by means of a truck or provided at the boarding gate
The craft generally employs a rectifier making it possible to provide a DC voltage from the AC bus to a high-voltage DC bus well known in the literature by the name “high voltage direct current”. The rectifier must be in particular compatible with the various generators that may power the AC bus.
In recent architectures, aircraft are becoming more and more electrical. In these architectures, certain loads of the craft are powered by converters with the help of the DC bus.
The multiplicity of generators making it possible to power the DC bus makes it necessary to dimension the linking equipment between a generator and the DC bus so as to limit, to within an acceptable span, the disturbances induced on the DC bus.
Moreover, the ground power units are generally rather intolerant to the disturbances rejected by the loads and notably by the rectifiers. International standards such as for example MIL STD 704 or ABD 100 define notably a span within which the voltage of the network must lie, a maximum rate of harmonics and a maximum imbalance between phases of the network.
It is moreover desirable to mutualize such linking equipment and to use for this purpose the rectifier powering the DC bus so as to provide the power to the DC bus with the help of any generator. This leads to this rectifier being dimensioned as a function of the generator that is most sensitive to disturbances.
Moreover, the quality of the power supply provided by the ground power units may vary from one airport to another.
To adapt to these various ground power units and to comply with the rates of rejected disturbances, provision must be made for appropriately dimensioned filters. These filters cause additional onboard weight. One of the aims of the invention is to reduce the dimensions of the filters associated with the mutualized linking equipment.
Another problem related to the multiplicity of generators is to maintain the aircraft's power supply without cutoff when a change of generator is effected, for example when the ground power unit is unplugged or else when the main generator replaces the auxiliary generator. The various generators are generally 115V or 230V AC generators with a frequency of 400 Hz. It is necessary to synchronize the frequencies and the phases of the generators during the change. Moreover, it is necessary to adapt the amplitudes of the voltages so that the power afforded by each can be correlated, this requiring delicate control of the various generators.
Another approach to cutoff-free transfer consists in rectifying the AC currents provided by the various generators (for example the ground unit and the auxiliary generator by 2 separate rectifiers). Cutoff-free connection is then carried out on the DC voltage after rectification. This approach no longer requires any synchronization in phase, frequency and amplitude of the AC generators, but uses rectifiers dedicated to the various generators, and requires high-voltage DC breakers.